This project is concerned with the detection and processing of sensations associated with the beating of the heart. Recently developed heart beat (HB) detection procedures yield data on the time intervals separating HB sensations from the onset of ventricular contractions. Experiments are proposed to account for reliable between-subject differences found in the temporal locations of heart teat sensations and in the precision of their detection. The two general categories of influence to be explored are (i) variations in cardiovascular activity which may generate the effective stimuli for HB sensations and (ii) individual difference factors identified by previous research to predict the ability to detect cardiac activity. The effects on HB detection of variations in cardiovascular activity will be explored by a combination of multiple regression techniques and experimental manipulations of cardiovascular performance. Multiple regression will also be used to examine the extent to which individual difference factors can predict performance on the HB detection task. Nervous system processing of cardiac afference will be studied by tow methods. The first is designed to differentially involve the right and left hemispheres in the solution of the HB detection task. The results of this experiment will be relevant to the hypothesis that the right hemisphere is preferentially implicated in the processing of cardiac afference and to the "Convergence-Projection" theory of referred visceral sensation. The second involves EEG recordings to explore the existence of subcortical and cortical HB-related potentials. Two future experiments are proposed. The first is designed to localize receptors involved in generating HB sensations by examining HB detection in individuals who have suffered selective lesions (spinal injury and heart transplant patients) in pathways which convey HB information to the sensory areas of the brain. The other will examine HB detection in patients who are symptomatic and asymptomatic for myocardial ischemia and in individuals who suffer "cardiac neurosis". This last proposal which examines pathological expressions of cardiac sensation identifies the health-related implications of the project.